Human bodies have some built-in systems to care for themselves. The cells that line our lungs, nose, brain and reproductive system have cilia, which are tiny, hair-like structures designed to sweep out fluids, cells and microbes to stay healthy. But the mechanisms behind their motion are not well understood.
A team of researchers in the McKelvey School of Engineering and the School of Medicine at Washington University in St. Louis wanted to determine how length affected the mechanical efficiency of beating cilia. They found that most mechanical metrics, including force, torque and power, increased in proportion to the length of the cilia, but there was a “sweet spot” in terms of efficiency. The findings give insight into cilia in humans and how defects lead to disease, such as primary ciliary dyskinesia, which is associated with chronic respiratory infections, changes in the right-left axis and heart defects. The results will be published in the April 9 issue of Biophysical Journal.
“Something we did not expect is that the short cilia would not be periodic,” Bottier said. “The cilia are all moving, but we find no actual pattern of beating — nothing was synchronized — and that was our first discovery.”
The study was led by Mathieu Bottier, a postdoctoral researcher in the lab of Philip Bayly, the Lilyan & E. Lisle Hughes Professor of Mechanical Engineering and chair of the Department of Mechanical Engineering & Materials Science; and the lab of Susan K. Dutcher, professor of genetics and of cell biology and physiology at the School of Medicine. The researchers used high-speed video microscopy to analyze a model for cilia to determine their mechanical metrics. After analyzing nearly 400 videos, the team found that the most efficient beating of cilia was at its natural length of 10-12 microns, or about one-fifth the width of a human hair.